Such a process has become known from EP-A 466,831. In this prior-art process, a resistor element with a catalytically active surface is exposed to the combustible gas mixture to be investigated, and the catalytic sensor is heated by a power source. The sensor is heated up during a first phase (heating phase) at constant current until a preselected resistance is reached. This resistance is maintained at a constant value during a second phase, until a steady state becomes established. The sensor remains switched off for a predetermined time during a subsequent, third phase. The voltage or the current in the steady state is used as the measured signal. Not only can the concentration of the combustible gas component in a gas mixture be determined according to the prior-art process, but information can also be provided on the type of gas over the duration of the heating phase.
However, as a rule, the determination of the duration of the heating phase is not sufficient for performing the gas measurement in a gas type-specific manner. In addition, it still remains necessary to enter a specific gas type factor into the evaluating unit when a multiple gas measuring device is to be used. The display unit of such a multiple gas measuring device is usually calibrated to one type of gas, so that the measurement of other types of gas requires a correction of this calibration value. These gas type factors are known to be calibrated to the sensitivity of methane when explosive gas mixtures are measured. The gas type factor of methane is thus set at one, so that other combustible gases have a gas type factor that is obtained from the quotient of the sensitivity of methane to the sensitivity of the gas or vapor to be investigated. As a result, a gas type factor of 1.9 is obtained for methanol, 1.5 for hydrogen, etc.